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Sunday - May 02, 2010

From: Austin, TX
Region: Southwest
Topic: Compost and Mulch, Planting, Soils, Trees
Title: Use of fresh clippings from tree trimmers for mulch in Austin
Answered by: Barbara Medford

QUESTION:

Hi, The tree trimmers are in my neighborhood (east central Austin) to clear the power lines and said I can have a load of free mulch. I am wondering if there is any harm in using the fresh mulch from our neighborhood trees in my flower beds and around our native trees. In particular, how likely is it that something in the mulch could harm my plants or big pecan trees (should I be worried about diseases or harmful/invasive seeds)? Also, we have been organic since we moved here 2 yrs ago -should I worry that local trees might have been sprayed with something nasty this spring that would end up in the mulch? Thanks!

ANSWER:

We once had a sweetgum stump ground out of a flower bed in our garden, and the plants, including roses, planted there after that were profuse and vigorous. The soil was soft and loose, and had all that good organic matter in it. On the other hand, this was our own tree, on our own property, and we watched the grinding being done. We knew about herbicide use (we didn't use it), diseases (there weren't any in the old tree) and had only cut it down because of the invasive roots of Liquidambar styraciflua (sweetgum). So, while we had a good experience, your points about the condition of the clippings are well taken. 

Our preference would be to compost the whole stack of stuff, adding nitrogen in the form of manure, cottonseed meal, or fresh green material. That would be a big project, taking a lot of space, and probably about two years, but it would remove most of the objections having to do with pesticides or diseases, as a hot enough compost pile will take care of about anything. However, you might be able to compost it in place, as it were, as long as you were conscious that the decomposition of the wood chip material would be taking away nutrients from the soil itself. Adding nitrogen-rich material to the top layer as the lower layer decomposed away would probably alleviate that. Whether something that coarsely ground would be acceptable in flower beds, we couldn't say, but you certainly couldn't put it on when you were expecting seedlings to come up, or plants that were cut back in the Fall to re-emerge, they would be smothered. 

Read this article from North Carolina University Mulching Trees and Shrubs, from which we extracted this paragraph:

"Properly composted wood chips can be used as a long lasting mulch that weathers to a silver-gray color. Unfortunately, most wood chip material is sold as a fresh material rather than as a composted or aged material. The chips decompose slowly, but as they decompose, microoorganisms use nutrients from the soil that might otherwise be available for plant growth."

 

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